Recently, a power supplying device using an SMPS (Switching Mode Power Supply) has received attention. The SMPS functions to stably supply power using a transformer and a switching device such as MOS FET (Metal Oxide Semiconductor Field Effect Transistor) and BJT (Bipolar Junction Transistor).
Meanwhile, as there is a tendency that home appliances are developed to be lighter and leaner, the SMPS is also required to be slim. A planar transformer is used widely in order to reduce the size of the transformer larger than any other circuit components of the SMPS.
However, since a conventional planar transformer used in an LCC resonant converter has a small leakage inductance, it is necessary to separately provide a leakage inductor at the outside thereof or separately use a core having a small magnetic permeability. Thus, there is a problem that a volume of the planar transformer becomes larger, or it becomes more complex to manufacture the planar transformer.